Pressure control device



Dec. 31, 1957 A, RAKE v Re. 24,410

PRESSURE comm. DEVICE Original Filed Ot. 11, 194B INVHVTOR Jaw/v A. 0244 a -cdifierent set of conditions. maintain the ratio P /P at a an improved gas pressure,

- control device of the United States Patent ()1 24,410 PRESSURE CONTROL DEVICE John A. Drake, Van Nuys, Califl, Aircraft Company, Van Nuys, o'f 'Californin Original No. 2,645,240, dated July 14, 1953, Serial vNo. 53,792, October 11, 1948. Application for reissue Auassignor to Marquardt 'Califl, a corporation gust 27, 1953, "Serial"No.'377,006

6-Clairns. '(Cl. 137--100) Matter enclosed in heavy brackets I] appears in the original patent but forms'no partof this reissue'specification; matter printed initalics indicates the additions "made "by reissue.

This invention relates to an apparatus and a method for controlling the ratio of gas pressure. Moreparticularly, it relates to apparatus and method for controlling the ratio of two gas pressures in a'process, or in an engine such as a jet engine.

It is frequently desirable in a process, orin the operation of an engine such as a'jet engine, to-exercise a control over two critical pressures and to maintain these pressures in a predetermined ratio. 'This can be accomplished by means of a flexible diaphragm, by exposing a part ofone side of the diaphragm to a vacuum and applying the pressures whic'hit is desired tocontrol to the unequal areas on-opposite sides of the diaphragm.

Mathematically stated, it P and F are the pressures which it is desired to regulate, and if the diaphragm areas to which these pressures are applied are 8 and S respectively, then the net force acting upon the diaphragm is nil if the pressures are such that the Equation 1 [or itsequivalent (l,)] is satisfied.

Iris-apparent that, by appropriately.selecting the values of S and S and by connecting the diaphragm with a valve or other means of cont-rolling one :or the other of the pressures, it is possible to provide continuous, automatic control of the pressures, "so as to maintain P /P at a selected value.

Such means, however, is difficult to adjust to satisfy Thus, it itisdesired to difierent value, .it is necessary to vary the value of S or S .Mechanical means of accomplishing this areposs'bl'e, but are awkward and diflicult to manipul-ate and nottoo accurate in theirper- --tormance.

It is an object of the present invention to provide pressure control-method and apparatus. lt a further object of the invention :to provide a device and a method of controlling the ratio of two gas stated in-other words, to .multiply a given such device being readily adjustable by pnuematic means to vary the pressure ratio without resort (to:mechanical-rneans tor-varying S and These and other objects of'the invention will abet-apparent trom the ensuing description and the appended claims.

-One term which the invention may assume is exemplified inathe tollowing description andillustrated by way of example in the .accompa-nying drawing, in-which the single figureis a diagrarrunat-ic representationof the invention .as applied to actuate a controls --one of the ,pressures.

the drawing the pressure control valve which, :in turn, Referring mow to to the central chamber 13 or pressure multiplying device comprises a gas-tight chamber 10, and disposed within such chamber is..a flexible diaphragm 11 and on one side thereof is provided a "bellows 12. The bellows 12 divides the space "to the left of the diaphragm into a central space or chamber 13 and an annular space 14, -.the 1atter space being maintained under high vacuum. The diaphragm area exposed is designated as S and the opposite'diaphragm area 'asS An inlet duct 15 is provided, opening into the righthand chamber 16 of the device and inlet and outlet conduits .17 and 18, respectively, are provided for the central chamber 13 in the le'fthand portion of the device. The inlet duct 17 is provided with a convergentdivergent or .choked section '19, having a throat area 3 and the .outlet duct is provided with a similar convergent-divergent or choked section 2.0, havinga throat area S this .latter throat area being variable by .means of a needle valve .21 having .apointer 22 and, .associa-ted the'rewith, a scale '23, which may be calibrated .for a "purpose explained hereinafter. .As also illustrated, -a rod or valve stem 36) .is secured 'at one end to thediaphragm 11 and at its other end to .a valve..3.1 disposed in a duct 3'2, which, for purposes of illustration, is indicated as a fuel duct. Y

In operation, the pressure control device functions as follows: The gases which it is desired to control are admitted to the ducts 15 and .17 and, of .course, that admitted to the central chamber 13 through.the duct 17 is vented through the outlet duct '18. Gas entering through the duct 15 and 'having .a pressure it, exerts upon the righthandside of diaphragm .113. iorce equal to P S The force exerted on the .lefthand side of the diaphragm'is-determined not onlyby the QgaS pressure R and the diaphragm area S but also by the throat areas 5;; and S of the choked sections 19 and "20. This .force may be regarded as the product .of an efiective pressure P in the chamber 13 and tthetal'ea i. 'e.,"P 'S I have discovered that a simple, linear relation exists between'the effectivepressure R and the variable throat area S Such relation exists when the li-nlet and outlet orifices are choked, .and the entrant pressure 3 15.511115- cie'n'tly high that sonic velocity 'is achieved in the throatsi,[s] areasS andS This condition tafqsonicwe- .l'ocity. flow at the throat ojan orifice is sometimesdefined as a choked condition of the orifice. Derivation of this linear relation follows:

The following mass flow parameter for the flow .of

a compressible fluid through an orifice can 'be .derived "from the basic laws of fluid mechanics:

T ztotal temperature process fluid P -=total pressure of process nun S='thro'at area of the orifice 'yr'ratio ofsp'ecific heatat'constant 'pressure to specific heat at constant volume o'ftheprocessffiuid "R=gas constant M=='Mach number, i. e. ratio of velocity of the process fluid'to speed "of sound in'theprocess fluid.

Provided the pressure is sutflcientlyf:l1igh,dihe?Mach numher vM at the throatof an orifice zefathe z-t ypeziliustrated in the drawing will berequa-lwto '1. Further, the-quantities 3R and T -may sbetregarded as-constants. "It thusifollows from Equation can be simplified as fol p where C is a constant.

from Equation 3,

2 that the'mass flow parameter lows;

Hence,

Inasmuch as S is constant and only 8,; is varied, this equation reduces It is thus apparent even further to the proportionality:

3 that, with a simple device such as illustrated in the drawing, and merely by manipulation of the needle valve 21, it

is possible to vary the outlet orifice area 8,; and thereby vary the etfective pressure P in chamber 13. 23, which is scanned It 1s also apparent that the scale by the pointer 22,

calibrated so as to indicate different values of P /P to maintain a dilTerent value of P /l this device 'Will be r valve 21 may be op a given v'alueof P /P the apparatus matically to .control decrease flow of '21 may be actuated directly or indirectly A practical application of the device "this invention is desc Serial No. 53,791, fi

fuel to an engine, so as the desired pressure ratio. Alternatively,

eadily apparent. erated manually,

the valve 31 2,641,105 dated June 9, 1953, entitled Temperature Control System, to complete details. scribed a system for which reference may be had for In the said application there is decontrolling the turbine inlet temperature of a turbojet engine, in which the fuel line is provided with a valve actuated by a flexible diaphragm a choked duct similar to the choked ducts I9 and 20 described above. needle valve whose expansive diaphragm temperature under consideration.

Many other applications out departing from the The outlet duct is controlled by a travel which is determined by a thermal is subjected to the process lined in the appended claims.

Having thus described my invention, what I claim and desire to secure by l. A pressure cont Letters Patent is: rol device comprising a chamber,

in communication therewith a pressure responsive member disposed therein presentmg opposite sides of areas S and 8;, means for introducing gas to one side of area S means separate from said first mentioned means and not in communication therewith for introducing gas to the other side of area S and means, for varying the efiective gas pressure exerted on area S said [means comprising] first mentioned means provided-with an inlet duct having a convergent-divergent section, an outlet duct having a convergent-divergent section, a gas source for supplying the gas to said inlet duct at a pressure sufiicient to cause sonic velocity flow at the throat of both sections, and a valve operable to vary the throat area of one of said sections.

2. A pressure control device comprising a chamber, a diaphragm disposed therein, a duct for admitting gas to one side of said diaphragm, and a gas inlet and a gas outlet each separate from said duct and not in communication therewith for admitting a gas to the opposite side and [a] another gas inlet and a gas outlet each separate from said duct and not for admitting a gas to theopposite side of said diaphragm and venting the gas therefrom, said inlet and outlet being each provided with side of the diaphragm [bellows] into a plurality of subchambers, the means for supplying fluid under pressure to one of said sub-chambers comprising a choked inlet and outlet.

6. A pressure control device comprising a chamber, a pressure-responsive diaphragm mounted in said chamber and dividing said chamber into a pair of sub-chambers, means for supplying fluid under pressure to one side of said diaphragm, means for limiting the effective pressure-responsive area of the other side of said diaphragm, said means including an annular bellows, means for admitting a compressible bellows including a choked inlet and means for permitting egress of fluid from said bellows comprising a choked outlet, the pressure of said admitted fluid being saflicient to achieve sonic velocity flow at the throat of both said inlet and outlet, and a valve for varying the effective area of said choked outlet, and valve means actuated by the movement of said bellows.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS Orr Apr. 17, 1900 Warren Apr. 11, 1905 Moller Oct. 6, 1914 Earl Apr. 4, 1916 Keith Dec. 28, 1920 Price Jan. 13, 1925 6 Campbell Jan. 1, 1929 Dolbey Jan. 3, 1933 Lorraine Aug. 18, 1936 Fischer Feb. 9, 1937 Cross June 1, 1937 Bailey Mar. 16, 1943 Quiroz June 1, 1943 Brockett Aug. 29, 1944 Beecher Apr. 24, 1945 Rosenberger Nov. 18, 1947 Swenson Aug. 1, 1950 Moore Apr. 17, 1951 Wyck0flf Oct. 9, 1951 

